The present invention relates to tape transport mechanisms, and more particularly, to a transport into which a tape cartridge is inserted, and a tape leader block is extracted and pulled to a take-up hub to thread the tape past a read/write transducer.
Winchester disk drives provide minicomputer systems with substantial data storage capacity and rapid data access. It is desirable to incorporate into such minicomputer systems auxiliary storage devices which utilize removable media in order to permit data interchange, archival storage and back-up protection. In many cases floppy disk drives are inadequate as auxiliary storage devices because only a relatively small amount of data can be stored on a single floppy disk.
Streaming tape drives offer a cost-effective solution to the foregoing needs. They are designed to operate at high speeds, enabling the transfer of large blocks of data between Winchester disks and magnetic tape. Unlike start-stop tape drives which require costly electro-mechanical components to start and stop the tape quickly in the gaps between individual blocks of recorded data, streaming tape drives simulate the start-stop function through a repositioning technique which eliminates the need for such costly electro-mechanical components. Streaming tape drives have heretofore been commercialized in models utilizing 1/2-inch and 1/4-inch magnetic tape. One example of such a drive is the FloppyTape (Trademark) drive sold by Cipher Data Products, Inc., the assignee of this application. It utilizes a dual-reel, 1/4-inch tape cartridge defined by ANSI standard X3.55-1977. The transport of the aforementioned drive is disclosed in U.S. Pat. No. 4,573,091 which is also owned by the assignee of this application.
Another tape cartridge suitable for use in an auxiliary storage device is defined in Proposed American National Standard X3B5/85-075. That cartridge contains a single reel of magnetic tape including a leader block for interfacing with an automatic threading system. The cartridge is more fully described in U.S. Pat. Nos. 4,335,858; 4,334,656; 4,383,660 and 4,452,406 and in U.S. Pat. application Ser. Nos. 315,112 and 315,120, both filed on Oct. 26, 1981. Said cartridge is hereafter referred to as the "leader block tape cartridge".
Currently a large percentage of minicomputers are designed to physically incorporate 5 1/4-inch Winchester and 5 1/4-inch floppy disk drives. These disk drives are constructed to meet an industry standard which requires that they fit within a rectangular volume measuring approximately five and three-quarter inches in width by three and one-quarter inches in height by eight inches in length. The foregoing set of dimensions are referred to in the computer industry as the 5 1/4-inch form factor.
It would be desirable to provide a magnetic tape transport that would fit within the 5 1/4-inch form factor and utilize the aforementioned leader block tape cartridge. Such a transport could then be inserted into the same physical enclosure or receptacle in minicomputers sized to receive the 5 1/4-inch Winchester and floppy disk drives. The IBM (Trademark) 3480 tape drive which utilizes the aforementioned leader block tape cartridge has a relatively large transport that will not fit within the 5 1/4-inch form factor. It uses a stationary magnetic head and a mechanism for moving the cartridge perpendicular to its plane into engagement with a drive chuck. U.S. Pat. No. 4,334,656 discloses a relatively large transport for the leader block tape cartridge. U.S. Pat. No. 4,335,858 discloses a transport for a leader block tape cartridge in which a flexible sprocketed guide ribbon is disposed in a continuous guide channel to carry the leader block along the tape path. The cartridge is moved vertically into engagement with the supply reel drive mechanism.
The aforementioned leader block tape cartridge has an outer cartridge box measuring approximately four and one-quarter inches in width by four and seven-eighths inches in length by fifteen-sixteenths of an inch in height. Any transport utilizing the leader block tape cartridge must allow sufficient space for a take-up hub that will carry a tape pack diameter of approximately three and three-quarter inches. In addition, the transport must receive and lock the cartridge in place upon insertion, extract the leader block from the cartridge, automatically thread the tape past the transducer to the take-up hub, and engage a supply reel motor with the cartridge. In addition, to obtain the desired data storage capacity such as 200 megabytes, data must be recorded serially on the tape in multiple tracks, e.g. twenty-four parallel tracks. Therefore a precision magnetic head positioning system is required.
Heretofore, persons skilled in the computer peripherals art believed that a tape transport for the leader block tape cartridge could not fit within the 5 1/4-inch form factor due to the relatively large size of the cartridge and the complexities involved in performing all the functions described above with a high degree of precision in such a confined space. The leader block tape cartridge and the take-up hub must be positioned in the same general plane. A skewed tape path which would result from mounting the supply reel and take-up hub in different planes would put undesirable stresses on the tape media which would contribute to error. The length of the 5 1/4-inch form factor is less than twice the length of the leader block tape cartridge and the width of the form factor is less than one and one-half times the width of the cartridge.
Accordingly, prior to our invention, nobody has been able to solve the space limitation problem inherent in attempting to fit a tape transport for the leader block tape cartridge into the 5 1/4-inch form factor. Also, the tolerances for tape guidance, azimuth control and head position control become extremely critical at the data densities required to store 200 megabytes or more of data onto the cartridge.